Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Micrograph Library Full Record for Micrograph 576

Full Record for Micrograph 576

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Micrograph no
576
Brief description
Injection-moulded protractor
Keywords
alignment, birefringence Link to MATTER Glossary entry for birefringence, injection moulding Link to MATTER Glossary entry for injection moulding, polymer Link to MATTER Glossary entry for polymer, polystyrene (PS), protractor, sprue, weld
Categories
Polymer
System
Polystyrene (PS)
Composition
Not specified
Standard codes
Reaction
Processing
Polystyrene was injected into a mould from a single point and has flowed round the component to meet at two noticeable 'weld lines'
Applications
Polystyrene is hard and inexpensive and its use is very widespread. CD cases and clear plastic cups are common examples. Domestic appliance casings are also typically made from PS
Sample preparation
Technique
Cross-polarised light microscopy
Length bar
30 mm
Further information
The colours in the image are the result of birefringence and relate to the residual strain in the polystyrene. The pattern of strain is indicative of the flow of material during the injection process and it highlights the injection point (at 152 degrees on the outer scale), and two 'weld lines' (at 338 and on the central bar) where two distinct flows of material meet. The weld line is a common point of failure because there is limited intermixing of the two fronts during the time allowed.
Contributor
J A Curran
Organisation
Department of Materials Science and Metallurgy, University of Cambridge
Date
03/10/02
Licence for re-use
Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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